drivers/mtd: Move conditional compilation to Makefile

rename CFG_FLASH_CFI_DRIVER to CONFIG_FLASH_CFI_DRIVER

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/README b/README
index d4456e5..37449d1 100644
--- a/README
+++ b/README
@@ -2064,7 +2064,7 @@
 		Define if the flash driver uses extra elements in the
 		common flash structure for storing flash geometry.
 
-- CFG_FLASH_CFI_DRIVER
+- CONFIG_FLASH_CFI_DRIVER
 		This option also enables the building of the cfi_flash driver
 		in the drivers directory